This invention relates to fluid brake systems for vehicles.
Conventional vehicle fluid brake systems are characterized by providing the ability for effective wheel braking in response to manual application of force to a brake pedal actuator.
A conventional vehicle fluid brake system includes a master cylinder which is connected by a piping system to brake calipers or wheel cylinders at each wheel. Movement of master cylinder pistons by a brake pedal actuator develops fluid pressure which is transmitted through the piping system to the wheel calipers or cylinders. Braking systems conventionally include a power source which utilizes either engine vacuum and atmospheric pressure or hydraulic pressure to provide power assist or "boost" to the master cylinder in applying fluid force to the braking system.
When a brake pedal is depressed, force is transferred by a push rod to the master cylinder primary piston which moves forward. Under normal conditions the combination of fluid pressure and the force of the primary piston's spring moves a secondary piston forward at the same time. When the pistons move forward, fluid is displaced until front and rear wheel brake linings contact the rotors or drums. Subsequently, hydraulic pressure is built up and transmitted to the front and rear wheels causing the brakes to be applied.
When the brake pedal actuator is released, fluid is forced back through the piping system to the master cylinder. Excess fluid returns to a reservoir which is generally mounted on top of the master cylinder.
The art has adapted conventional vehicle fluid brake systems as thus far described to automatic control mechanisms which intervene in the event of certain conditions and provide advanced braking functions. One such mechanism, an anti-lock braking system (ABS), generally represents a combination of hydraulic and electric control.
A typical ABS system inhibits the vehicle's wheel brakes from locking up by releasing the applied fluid pressure when an incipient wheel lockup condition is sensed. After release of the fluid pressure wheel deceleration ceases and the wheel begins accelerating toward vehicle speed. When the wheel speed has substantially recovered braking fluid pressure is reapplied. Reapplication of fluid pressure can result in the wheel again approaching lockup and therefore, the cycle is repeatable.
The art has proposed that ABS functions can be provided by employing several different mechanisms. The problem posed in developing an ABS braking system is to provide optimum operation considering system response, adaptability and efficiency while concurrently avoiding unnecessary complexity and cost. This presents a significant challenge in the development of vehicle braking systems.